难加工材料被切除表面层合金添加晶界弱化机理及其应用基础研究

Improving the machinability of difficult-to-machine materials is the foundation to realize the high efficiency and high quality machining process. In addition to improving the cutting tool properties and the cutting technologies, the problem of poor machinability for difficult-to-machine materials can be solved radically through changing the microstructure and mechanical property of the removed layer. The project aims at exploring the research feasibility through alloy addition to weaken the material removed layer and improve the machinability of difficult-to-machine materials. The material of GH4169 is selected as the research object which is one kind of typical difficult-to-machine materials. The rare earth elements and harmful impurity elements such as S and P are selected as the infiltration elements. The effects of alloy infiltration on the evolutions of microstructure and property of GH4169 are investigated. The grain boundary weakening mechanism of alloy addition into the difficult-to-machine materials is revealed. Then the removed layer of workpiece material GH4169 is weakened through alloy infiltration process. The technological procedures of alloy infiltration are optimized to control the alloy infiltration thickness (50μm-1000μm) and the alloy infiltration content quantitatively. Based on the cutting experiments, the material removal mechanism for alloy infiltration layer of GH4169 is clarified. The formation of fragmented chip for GH4169 under conventional cutting conditions is realized. The relationships among “alloy infiltration - material microstructure and mechanical property - material removal mechanism - machinability” are established. The research provides a theoretical and practical foundation for the machinability improvement and high efficiency removal of difficult-to-machine materials.

改善难加工材料切削加工性是实现其高效率和高精度加工的基础，除了改进刀具性能和切削工艺之外，通过改变工件材料被切除层的组织结构与力学性能，可从根本上解决其切削加工性差的难题。项目以镍基高温合金GH4169为研究对象，探索通过合金元素添加“弱化”工件材料表层从而改善其切削加工性的实现方案。以表面渗合金工艺为技术手段，以稀土元素和有害杂质元素（S、P等）作为渗入对象，研究渗合金处理对GH4169微观组织与力学性能的影响规律，揭示合金元素对工件材料的晶界弱化机理，实现对工件材料被切除层的弱化处理，并制定满足渗合金层厚度（50μm-1000μm）及合金元素含量定量控制的渗合金工艺规程；研究工件材料渗合金层的切削去除机理，实现GH4169在常规切削条件下碎断切屑的形成，构建难加工材料“合金元素添加—微观组织与力学性能演化—材料切除机理—切削加工性”的映射关系，为实现其高效切除提供理论支撑和应用基础。

改善难加工材料切削加工性是实现其高效率和高精度加工的基础，除了改进刀具性能和切削工艺之外，通过改变材料被切除层的组织结构与力学性能，可从根本上解决其切削加工性差的难题。本项目以镍基高温合金GH4169为研究对象，创新性提出了利用合金元素添加“弱化”工件材料表层从而改善其切削加工性的实现方案，具体包括高温固态渗合金弱化处理工艺和离子渗合金弱化处理工艺。以表面渗合金工艺为技术手段，以有害杂质元素（元素Te和元素S）作为渗入对象，研究了渗合金处理对GH4169微观组织与力学性能的影响规律，揭示了合金元素添加对工件材料的晶界弱化机理，实现了GH4169弥散强化相向晶间弱化相的定向转变；结果表明渗入Te元素后能够在工件材料原有晶间强化相处与基体元素发生化学反应而形成碲化物或氧化物等弱化相，并在晶界处诱导形成裂纹或孔隙等缺陷，有效实现了对工件材料被切除表面层的弱化处理，并基于上述研究结果制定了弱化层厚度和弱化程度定量控制的渗合金工艺规程；利用微米刻划模拟切削和直角切削实验对比分析了工件材料渗合金弱化处理前后的切削去除机理，实现了GH4169在常规切削条件下碎断切屑的形成和高效切除，使切削力和切削能耗得到有效降低、表面加工质量得到提高；最后构建了难加工材料“合金元素添加—微观组织与力学性能演化—材料切除机理—切削加工性”的映射关系，从根本上改善了难加工材料的切削加工性，为实现其高效切除以及高性能易加工材料的成分设计提供了理论支撑和应用基础。